The present invention relates to an improved guide for a hand held power cutting tool and, more particularly, to a guide for a hand held power cutting tool of the type having a blade extending through a base plate and wherein the guide is adjustable to compensate for an offset distance between an edge of the base plate and the blade of the cutting tool.
Conventional carpentry practice in cutting a board is first to utilize a square and/or ruler to position and then mark the intended line of cut. The workman then manually aligns the blade of the saw, sighting through the opening in the saw platform, and aligns the blade with the scribed line. The workman then begins cutting, maintaining alignment by making minute corrections as required. The vibration of the saw, and the binding effect of corrections limits the ability to track the line after any deviation. Thus, even experienced carpenters will at times deviate from the intended line by an amount sufficient to make the completed parts unusable.
If an attempt is made to correct the deficiencies of the manual technique by utilizing the edge of the saw platform as a follower, then additional time consuming steps must be taken. A straight edge must be secured into position at the right distance from the scribed line. This distance must be determined by measurement or experimentation and is difficult to plot accurately. Then the straight edge must be clamped or otherwise mechanically secured in position.
Numerous types of guides for use in connection with hand held power-cutting tools are known in the art. Many such prior art devices, however, have the disadvantages of being unduly complicated and often difficult to use. Other such prior art devices encounter difficulties in aligning the guide device in spaced relation to the desired cut line to allow for the distance between the blade and the edge of the base plate through which the blade extends.
There have been various types of guide apparatus for power tools having blades such as sabre saws and circular saws. Most of the guide apparatus for the saws have included an integral guide channel secured to the base plate of the saw. The channel cooperates with a guide flange secured to either a table or to the work which is to be sawed. Typically, the guide apparatus of the prior art includes an upwardly extending flange which is secured adjacent to the desired cut at a fixed distance therefrom. The saw, with its guide channel inverted so as to receive the upwardly extending flange, is placed on the guide apparatus with the channel and flange matingly engaged for movement only along the channel. The saw is then guided as the channel moves along the flange. In some cases, there is a guide channel on each side of the sole plate or shoe of the saw.
Since the guide channel is integral with the sole plate or shoe, each saw must have its own respective sole plate or shoe for use with the guided apparatus. That is the guide apparatus is designed and adaptable only to one specific make of saw. The prior art does not include a universal guide apparatus, which can be used with virtually any saw. Since the sole plates or shoes of the saws include guide channels, the manufacturers of the saws themselves must include the guide apparatus with the basic saw since the sole plate or shoe is normally not a replaceable item separate and apart from the saw itself. The sole plate or shoe of a saw is normally secured to the saw housing and motor as an integral part thereof, and is not normally replaceable. Accordingly, it is necessary that each manufacturer of saws include some type of guide apparatus either as an optional configuration of a saw or else as a standard item with the saw. If the saw is not to be used with the guide apparatus, nevertheless the guide channels are a part of the saw in prior art apparatus.
One of the inherent problems associated with the development of a universal carrier and guide channel apparatus to fit a number of different saws has been the multiplicity of designs of saw sole plates or shoes. The width of the sole plate or shoe varies from about 2xe2x85x9 inches to about 2xe2x85x9e inches for the most common sabre saws. However, there are circle saws that vary in width from 3xc2xc inches to 4 inches, and up to about 5xc2xd inches. Moreover, some of the shoes are curved upwardly at the front end, and some are flat without any upward curvature. Some have upwardly extending lips on the side edges of the shoes while others are flat. All in all, it appears that there are almost as many variations in cutting tool sole plates, or shoes, as there are manufacturers of cutting tools, or even more due to variations between models by the same manufacturer.
An object of the invention is to provide a guide for hand held power cutting tools of various sizes and in which means are provided to position the straight edge of the guide a predetermined distance from a desired cut line, depending on the offset position of the blade extending through the base plate.
Another object of this invention is to provide a guide for a hand held power cutting tool in which the guide is easily positioned on a work piece to be cut and the straight edge of the guide indexed while the guide remains on the work piece so as to accommodate the offset position of the blade relative to the base plate of the cutting tool such that the mating of the edge of the base plate with the straight edge or fence of the guide assures a straight and accurate cut.
The present invention achieves the above and other objects by providing a guide for a hand held power cutting tool of the type having a blade extending through a base plate wherein the guide is adjustable on the work piece to compensate for an offset distance between an edge of the base plate and the blade. The guide comprises an assembly that includes a carriage which is movable and a carriage stop which is adjustable relative to the end of the carriage. The distance between the carriage stop and the end of the carriage is adjusted to equal the offset between the saw blade and the end of the base plate of the saw. The assembly further includes a straight edge or fence that mates with the edge of the base or sole plate of the cutting tool to allow a straight cut. A non-skid surface is attached to the underside of the carriage and placed against the work piece to attach the carriage to the work piece without any external clamping device and the like and allows the assembly including the straight edge and carriage stop to move relative to the carriage. Once the carriage stop is adjusted from the end of the carriage to a distance equal to the offset of the blade relative to the base plate, the straight edge of the guide is placed on the cut line. Movement of the assembly away from the cut line and relative to the carriage until the carriage stop contacts the end of the carriage places the straight edge of the guide at the correct offset distance. Mating the base plate of the saw with the straight edge of the guide allows an accurate and straight cut across the work piece. The guide optionally includes means to adjust for the thickness (kerf) of the blade. This enables the user to place the resultant kerf of the blade on either side of a point where the cut is desired.